Apparatus for mine roof control



July 3, 1956 J. F. JOY

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lzvenor:

nited States Patent arranarns ron Miren noon CoNrnoL Joseph F. icy, Pittsburgh, Pa., assignor to Joy Manufae: turing Company, Pittsburgh, Pa., a corporation or Pennsylvania Application October o, 1945, Serial No. 53,670

13 Claims. (Cl. 61-45) My invention relates to apparatus for mine roof control.

Roof control is one of the most expensive and troublesome items in mining. This is true both because of the expense of the materials which have been used and because so much of the materials employed is lost as a result of roof subsidence as the working face advances. This is also true because of the large amount of labor involved in building cribs, setting timbers, etc. Thus, the provision of an efective and rapidly adjustable means for effecting roof controlone that is relatively secure against-loss of its elements and which can be used over long periods-is highly desirable, and this is true whether or not such devices are employed with long or short faces.

ln my application, Serial No. 24,574, led May l, 1948, now matured into Patent No. 2,714,505, and granted August 2, i955, I have disclosed several roof control arrangements and methods of roof control, and in this present application I shall describe inventions which from certain aspects mark basic improvements in their provision of a support which can yield, in the event increasing roof pressure makes that necessary, and then return to prior support height when advanced to a point where the roof pressure is within the original setting of the apparatus, all without manual adjustment of the volume of liquid in the roof jack devices employed-to mention one such improvement, and which inventions also include various other structural improvements. The foregoing specifically mentioned features are not exclusive, or intended to be a complete listing, as will appear as this specification proceeds and the appended claims are perused.

While the present invention is ,in no sense limited to such a system, its understanding may be facilitated by considering its application to an advancing system of longwall mining in connection with which the strata overlying the mined out area opposite the face are permitted to cave in completely, in the areas between the customary roadway packs, except for the strip or space adjacent the face used for mining and working purposes. Its use in such a system is therefore illustrated and will be described by way of example.

An object of my invention is to provide an improved and dependable means for resisting the closing of the gap caused in the earths strata by the removal of certain layers thereof, such as coal seams or the like, for a sufficient length of time to permit the mining of said layers. Another object is to provide an improved roofsupporting structure having means incorporated therein for facilitating its being progressively advanced, along with the advance of a mine face, without substantial release of the resistance to roof subsidence and with sufcient yield provided for automatically to accommodate at least minor local subsidences. Still another object is to provide improved mechanically actuated structures for the control of mine roofs which support the roof close up to the face alongtheroof'Y line. and sufficiently to the v 2,752,77 Alliiatented July 3, 1956 rear of the face at the floor line for the elcient operation of coal producing apparatus. It is a further 0bjeet to provide an improved roof jack mechanism. Still another object of the invention is to provide an improved roof control system adapted particularly but not exclutively to the control of mine roofs along long faces. Another object is to provide an improved roof jack mechanism which shall permit jack adjustment without interruption of roof support, and this notwithstanding the fact that there may be some irregularity in roof level and in roof-exerted pressure. Still a further object of my invention is to provide an improved roof jack mechanism of the hydraulic type having incorporated therein means for providing for a limited degree of yield without venting of hydraulic fluid. Yet another object is to provide an improved roof control system having the advantages of hydraulic control together with resilient yielding through the conjoint use of an entrapped body of gaseous fluid. A further object of the invention is to provide an improved roof jack incorporating improved means for permitting the same to adjust itself to unequal roof pressures. Still another object is to provide an improved roof jack structure having incorporated therein an improved arrangement for facilitating its repositioning without interrupting its supporting action, that is, while it is yet sustaining the pressure of the roof. Another object is to provide an improved plurally articulated roof jack structure. Still another object is to provide an improved jack mechanism including improved means for etfecting resilient yielding thereof at roof pressures below a predetermined value and adapted to permit relief through the discharge of Huid in the event of pressures great enough to endanger the structure providing the resilient yield. Another object is to provide improved means for associating a plurality of roof jacks together. Still another object is to provide an improved roof jack mechanism having improved means for shielding a conveyor mechanism which operates in the space between the floor engaging portions of the roof jack mechanism and the coal face. A further object is to provide roof an improved jack mechanism having improved means for altering its line of advance. Other objects and advantages of the invention will hereinafter more fully appear.

In the accompanying drawings, in which for purposes of illustration I have shown two embodiments which my invention may assume in practice,

Fig. l is a horizontal sectional view through a mine at and adjacent to a longwall working face, showing one of the illustrative embodiments of the invention, parts being omitted to avoid complication.

Fig. 2 is an enlarged plan view of one illustrative embodiment of my improved roof jack structure, with parts broken away and/ or omitted.

Fig. 3- is a side elevational View of the structure of Fig. 2, likewise with parts broken away and/ or omitted.

Fig. 4 is a further. enlarged, fragmentary, vertical sectional view on the plane of the line 4-4 of Fig. 2

Fig. 5 is a transverse vertical sectional view on the plane of the line 5 5 of Fig. 2, showing details of construction of one of the roof supporting jacks.

Fig. 6 is an enlarged generally horizontal sectional view on the plane of the line 6 6 of Fig. 3.

Fig. 7 is a View corresponding generally to Fig. 2 showing a modified form of construction. l

Fig. 8 is a side elevational view of the structure shown in Fig. 7.

Fig. 9 is a vertical sectional view through the earths strata, including a coal seam and portions of underlying and overlying material, and showing one of the illustrative embodiments of my improved walking jack mecha- -nisminu'se Fig. l() is a. detail sectional view on the plane of the line -10 of Fig. 3, with parts omitted.

Fig. 1l is a similar view, showing a conveyor-pushing buffer connecting and supported by the opposite forward en ds of the forward wheel supported frame.

Fig. 12 is a somewhat diagrammatic view showing the uid pressure operating sources and connections for electing the roof-supporting and walking operation of the jacks.

Fig. 13 is a fragmentary sectional view through the bottom end of a pump used to supply uid to the rootsupporting jacks.

Referring rst brieily to Fig. l, it will be noted that a longwall face is illustrated at 1. This includes a portion 1A which has been advanced one cut of a mining machine 2. beyond the portion 1B which still remains to be advanced to a position in. alinement with the portion 1A. The mining machine 2 may obviously assume various forms, and as shown has suitable mechanism 3 'for disintegrating, or for cutting so that the pressure may disintegrate, the coal. The face 1 has at its opposite ends stalls 4 and 5, andV roadways 6, provided for ventilation and coal removal purposes, communicate With the stalls. These. roadways are held open by roadway pack walls 7, and as the system of mining illustrated is intended to operate according to the substantially complete caving method, the roof is indicated at 8 as having caved between the adjacent sides of the roadway pack walls. A conveyor 9, which may assume various forms such, for example, but Without limitation thereto, as one shown in Figs. to 24 of my pending application above identified, extends for the full length of the face, being spaced therefrom only by the necessary distance to permit the handling of the coal cutting or disintegrating equipment, and extending also pretty well across the spaces at the mouths of the stalis 4 and 5 and into close adjacency to a conveyor C leading out of the section of the mine from which coal is being taken out. Itis unnecessary, for the purposes of this case, to describe the means for extending the stalls and maintaining them in advance of the actual working face. The conveyor 9 may be driven in the manner disclosed in my earlier application, but may be driven by any suitable means, and so no drive therefor is illustrated. The conveyor is illustrated as of the articulated type so that portions of it may be advanced. relative to other portions while the conveying operation progresses, and numerous structures of this character are known to the art. To prevent roof subsidence both in the stalls and along the working face, I have provided rooi'i jack mechanisms which are generally designated 20 andv these,` by their con.-

struction and spacing,A are adapted to hold the roof from caving except in the manner and to the extent desired.

The jack structures of' the embodiment of the invention first to be described are best disclosed in Figs. 2 and 3, from the standpoint oi comprehensive illustration, and the details of their construction. may be noted. in Figs. 4,. 5, 6 and l0.

Referring now to Figs. 2, 3, 4, S and 6, it willv be noted that the apparatus shown includes front andL rear roof load sustaining jack structures, generally designated 21 and. 22, an abutment jack 23, expansihle chamber means 24j for imparting repositioning forces to the jack' structure 21, and connecting means generally designated 26 for causing thejack.y structure 22 to advance with the jack structure 21, `while enablingl relative movement' between the two jackv structures 21 and' 22. Marry of the parts of the front and rear jack structures are* identical, and theyare reversed, in assembly, to form the. jack structure 22, from their positions in the, jack structure 21` The adjustable connecting means 26 provides for changes both in spacing and in horizontal and vertical angles between the jack structures 21 and 22..

The jackstmctures 21, and 22 includemeans, 3l, 31', for supporting them for movement over the mine door;

means, 32, 32', engageable with the mine roorandjack' devices, 33, 33', for forcing the oor and roof-engaging means apart to provide the requisite roof support.

The floor-engaging supporting means 31 includes a transverse frame member 35 recessed at 36 to support the lower end of the roof-support-pressure-providing means 33, and having at its opposite ends respectively as shown in Figs. 5 andA l0, at one side a'rigid (herein shown as integral) connection with a wheel mounted frame 37 and at its opposite side a pivotal connection 38 with another wheel mounted frame 39. The latter connection is provided by a stub shaft 40 xedly mounted as at 41 in one end of the cross frame 35 and pivotally supporting the wheel mounted frame 39, in a bore 42 in which it is received. An enlarged head 43 on the pin 40 prevents sliding of the frame 39 oli. of the pin 40. The frame 31 is correspondingly, but reversely, formed.

The upper mine roof-engaging means 32 includes (see Figs. 2, 3 and 5) a transverse frame element 45 having a recess 46 adapted to receive the upper end of the device 33, and having an integral. connection at one end thereof with a wheel supporting frame. 47, while having at its other end a pivotal support 48 for a wheel supporting frame 49, similar in construction to the pivotal support for the frame 39. The frame 32 is correspondingly, but reversely, formed. The frame element is capable of limited pivotal movement upon the upper end of the device 33, as is the corresponding frame-` element on the device 33', so that both front to back and lateral tilts are possible.

The means 33 for forcing the oor and roof engaging meansy 31 and 32 apart and providing the desired support for the roof is shown as of the hydraulic pressure operated type. It. includes a tubular member S1 constituting a cylinder, and having connected thereto, as by welding, a lower head 52, having a projecting boss or pluglike element 53 welded in an opening S4 formed in the bottom wall 55 of the recess 36. Within the cylinder element 51 there isl reciprocable a hollow piston element 57, comprising a sleeve or tubular member 58, of which the diameter is' substantially the same as the diameter of the bore of the tubular element 51, said member 58k having secured thereto an upper head 59 having a bossv or projection 60 received in an opening 61 formed in the top wall 62 of the frame member 45 at the upper end of therecess 46. The member 59 is suitably connected, as by Welding, to the sleeve member S8. At the lower end ofthe sleeve member 58 there isv a. suitably packed piston 64, shown as provided with a chevron packing 65, and connected, as by welding, at 6 6 to the lower end of the tubular member 58. The piston member 64` is recessed at 68 in its lower side, and; a bore 69 extends. from the top of the recess 68 through the upper surface of the piston 64, and is internally threaded as at 70 to provide a mounting for an accumulator 71 which may be, for example, of the Greer type. This accumulator 71, as illustrated, is shown as including* a shell 72, and a separator bag or bladder 73 providing a chamber 74 in which a compressed fluid such as air or nitrogen is confined. The separator bag or bladder may be made of any suitable material, for example, a synthetic material such as neoprene may desirably be employed because it resists destruction by the action ofoil upon, it.

IShe mouth of the accumulator has mounted in it a suitable ported' metal plug 7'5, with which a cone-shaped metalplug 76, molded into theA heel,A of the bag, isadapted tocooperate, when. the pressure within the device 33 becomes low enough, to prevent extrusion of the bag through thel plug 75. A suitable iilling connection for the bag is provided. at177 through which the bag may be preloaded-.withz air, or preferablynitrogen, from anexternal supply, before. thejackl mechanism is assembled.

Enom; whatA has'. beem said, it; will be appreciated'` that the-spaced@ helowitheipistoir element. 64 isdn free-com munication with the interior of the shell 72 when the pressure in the chamber 36 exceeds the pre-established pressure in the space 74 within the bag 73. There is associated with the frames 31 and 32 a hydraulic jack device 33', as previously noted, and this is of essentially like construction as the jack device 33.

The supply of uid to the spaces 80 and S0' within the jack devices 33 and 33' is by a hand operated pump mechanism, and it will be noted that a shelf 89 carried by the frame 35 supports a pump mechanism 96. This may be of any suitable construction, and, as shown, includes a casing 91 in which there is a reservoir 92, and a pump cylinder 93 in which a plunger 94 is adapted to be reciprocated by a suitably arranged pivoted lever mechanism 95. The bottom of the pump cylinder communicates through a passage 96 with a chamber 97 which is arranged between a pair of check valves 98 and 99. The check valve 99 controls communication with the discharge line 100, which opens into a valve casing 101. The check valve 98 controls communication between the reservoir 92 and the chamber 97. The valve casing 101 contains a valve (not shown) shiftabie to connect the line 166 with a conduit 104, leading to the chamber S associated with the forward roof-supporting jack cylinder 33, or to connect the line 100 with a conduit 165 leading to the chamber 80 in the jack mechanism associated with the roof support mechanism 22, or to connect the line 100 with both conduits at the same time. A return connection from the line 100 to the reservoir is provided at 106 and is controlled by a valve 167. The reservoir has a supply connection 108, and additional fluid may be supplied to the reservoir, if needed, while the jack devices are being extended to provide approximately the desired elevation of their upper portions. Means for releasing pressure from the spaces 80 and 89' in the event of excessive roof pressures is provided in the form of two relief valve controlled means 1199 and 109', these having the relief valves therein set at pressures higher than any normally desired pressure in the chambers 89 and 80 but adapted to permit the return of fluid from these chambers through a common conduit 110 to the line 166 if pressures such as to endanger the accumulators is occasioned by markedly increased roof pressure. Other control mechanism will be described after a further description of the walking jack mechanism structures, and in connection with Fig. 12.

The frames 31 and 31 and 32 and 32 are each provided with closed-ended yoke portions as at 111, and within the openings 112 within these yoke portions there are rotatably supported wheels 113 which are mounted upon cross shafts 114 mounted in bosses 115 carried at the opposite sides of the yoke frames 111. These wheels are provided with solid rubber tires 116 which are so made that, as illustrated in Figs. 3 and 4, and on a smaller scale in Fig. 9, they may be considerably flattened at their points of engagement with the floor and roof so as to provide relatively large areas of contact between their peripheries and the oor and roof, thus reducing the pressure per square inch of contact, and yet be capable of rolling without excessive forces being required.

The wheel supporting frames associated with the front roof-supporting jack 21 and with the rear roof-supporting jack 22 are connected together by suitable mutually independently adjustable connecting means, herein illustrated as tunbuckle mechanisms 120, whose opposite end members 121 and 122 have eyes 123 loosely surrounding pins 124 carried by spaced flanges 125 formed on the adjacent ends of said frames. Like connections extend between the lower wheel-supported frames. Thus, the forward movement of the jack device 21 will be attended by forward movement of the jack device 22. Changes may be made in the spacing and in the angle of jack device 21 relative to the jack device 22 and yet, if there isuneven subsidence of the roof, there may be a tilting of say the rear frame 32' relative tothefront frame 3 2.V

6 Change in the direction of jack travel may also be facilitated, as later explained.

The abutment jack 23 includes a cylinder 131 closed at its bottom as at 132 and having a mine floor-engaging underlying support element 133. Within the bore 134 of the cylinder there is reciprocable a piston 135 having a suitable packing 136, and connected to a tubular member 137 which carries a roof-engaging element 138 at its upper end. Fluid may be admitted to and vented from the space 139 beneath the piston 135 through a conduit 14d, and the means for supplying and venting this uid will shortly be explained. The device 24 for effecting walking operation of the jack mechanism includes a cylinder 145 having a bore 146 and opposite heads 147 and 14S. The head 147 is traversed by a hollow piston rod 149 which carries a suitably packed piston 150 at its forward end and which, at its rearward end, is threadedly connected as at 151 with a boss 152 on a collarlike element 153 surrounding the cylinder 131. The head 143 is connected by an ear 155 and a cross pin 156 with ears 157 formed on a collar 153 surrounding the cylinder element 51. By suitably iixing, as by clamping (member 153 is split, to enable clamping action) the collar element 153 against upward or downward movement along the cylinder element 131, lowering of the collar element 158 may be prevented.

Fluid may be supplied to the uid supply conduit through a passage 159 formed in the cylinder head 14S and leading to the bore of a tube 161B mounted at 161 in the head 148 and telescoping with the hollow piston rod 149, the conduit 140 opening into a bore in the piston rod 149, which bore receives the tube 160. Fluid may be admitted to the opposite ends of the cylinder bore 146 through conduits 165, 166 formed in the cylinder heads 148, 147 respectively. Each of the uid supply connections 159, 165 and 166 will desirably be equipped with a fitting through which fluid can be supplied to it past a stop valve, but these connections will be more fully described later. v i

In view of the fact that the jack device 23 and the walking cylinder and piston mechanism 2d will have iluid supplied to them and vented from them only on the order of perhaps once or twice-or at most a very small number of timesa day, it is unnecessary to provide liuid reservoirs and pumps individually to them, and instead a portable fluid supply and discharge arrangement such as is shown in my Patent No. 1,900,446 may be provided to supply fluid to extend the abutment jack 23 and to move the cylinder relative to the abutment jack, or to allow the venting of duid, it being understood with respect to the device 24 that it will be necessary to provide a return connection from whichever one of the connections or 166 is not to have Huid discharged to it from the apparatus shown in said I oy patent. Such a fluid supply means is portable from jack to jack.

The rearward end of the frame 32--the rearward ends of the rearward wheel supports N11-have upstanding ears 169 upon them between which there is pivotally supported a mounting 171i' for an inclined fender rail 171. These inclined rails 171 prevent a liow of roof fragments beneath the rearward roof-supporting elements from interfering with the jack mechanism and also exert forward thrust on the rearward jack when engaged by a subsiding roof, and thus make the walking operation easier and prevent the roof from pinching the jacks. The rails 171 may simply slidably engage the mine bottom at their lower ends. Simiiar ear arrangements 173 are provided at the forward end of the wheel frames 32 at the front end of the jacks 21, and these carry pivotally mounted between them a generally L-shaped frame 174 having a forward portion 17S and a downwardly depending portion 176. An adjusting screw mechanism 177 extends between each downwardly projecting portion and the forward end of the adjacent frame portions 111, and permits control of the level lor inclination of the forwardlyprojecting frame portion 175, which extends nearly to the face and provides additional protection for the underlying conveyor. The outermost end of the forwardly extending portions 175 carry rail sections 178 which increase the roof-supporting action.

In Fig. 12 there is shown for purposes of illustration a control diagram. This shows the connections so far mentioned, and also others. The roof jack devices are shown at 33 and 33', the abutment jack at 23, and the double acting cylinder and piston mechanism for eiiecting walking is shown at 24. The abutment jaclf. and the walking mechanism are adapted to be supplied with hydraulic fluid under pressure from a separate power driven pump device 180, such as is shown in my Patent No. 1,900,446. The only material difference between the device of the patent and the device shown at 181i, resides in the fact that a return conduit or connection 131 is provided for the back flow of fluid from a working space which is to be vented to the reservoir of the device 18), and of course the reservoir size and the discharge pressure will be predetermined to the demands of the work to be done. lf desired an adjustably loaded relief valve 182 may be arranged between the discharge conduit 183 from the device 180 and the return line to the reservoir. Each of the connections 159, 165 and 166 will be provided with a stop valve (shown in Fig. 12 at 134, 185 and 185), and suitable quick detachable connections, as of the Hansen coupling type, may be provided to facilitate connection and disconnection between the conduits 191 and 183 and the connections 159, 165 and 166.

The iluid supply to the roof jack devices 33 and 33 is, as has been previously noted, such that uid may be supplied simultaneously to them, as will ordinarily be desirable, .or separately, and fluid may also be vented simultaneously or separately from them. The manually operated pump mechanism 9i) supported by the jack device 21 includes, as has been noted, a reservoir 92., a pump cylinder 93, and manual operating means 95 for the pump. The mechanical advantage of the pump operating means and the cross sectional area of the pump cylinder will be made such as to enable an operator without excessive exertion to pump up the desired pressures in the jack devices 33 and 33.

Before discussing the general mode of operation of the walking jacks so far described, a brief discussion of the roof jack cylinders and accumulators may be helpful. It will be appreciated that to all practical intents and purposes the pressure per square inch below one of the roof jack pistons and the pressure within the accumulator housed in the piston tube member will be at all times equal when the pressure below the piston exceeds the preload pressure within the accumulator bag. The diam eter of the piston will be so chosen as to enable the product of the ettective area of the lower face of the piston, multiplied by the hydraulic pressure applied thereto, to equal the normal desired roof supporting pressure cumulatively exerted by the four wheels, plus the Weight of the parts of the jack device lifted by hydraulic pressure. The last item, though substantial in itself, is a very slight element of the total load sustained by the hydraulic huid. As seams run frequently quite uniform in thickness, and as the thickness of the removed coal may be even more uniform, the degree of upward movement of the jack piston can bc rather definitely determined, and hence the displacement of the piston as it is moved upward by the hydraulic fluid and forces the wheels with requisite pressure against the root' may also be predetermined rather definitely. Now, it may be desired to preload the accumulator bag with nitrogen or other gaseous uid under pressure, either to a substantial fraction of, or to the full vaine of, the pressure at `which the hydraulic fluid will normally be during roof support. lf the roof pressure increases to such an extent that the cntrapped hydraulic tluid will be subjected to a pressure greater than that to which it was subjected to provide the desired roof support, then more of it, or some of it, as the case may be, will flow into the shell of the accumulator and increase the pressure of the gaseous fluid in the bag. lf the range of potential downward movement of the piston be such that the pressure exerted on the accumulator bag will exceed the safe Working limit of the latter, before the piston reaches the lower cylinder head, a relief valve can be provided as a safety measure, but if the piston head would reach the cylinder head before the pressure of the gas within the accumulator bag would reach the danger zone, a relief valve, though provided, would release no hydraulic fluid back to the reservoir. In practice, the roof-supporting pressures will be so adequate that seldom will the roof pressure attain to values which cannot be adequately supported by the jack as it yields and is automatically subjected to increased supporting pressure by reason of the increase in pressure of the confined gas' in the accumulator, without venting to the tank of liquid; and, when the roof-engaging portions of the jack move ahead to an area of lower roof pressure, the gas in the bag would reexpand, and normal roof-supporting pressure would again be applied. From the foregoing it will be evident that by properly selecting roof jacks of a collapsed height near the thickness of the coal to be removed and predetermining the accumulator volume with proper regard to the maximum displacement under hydraulic pressure of the roof-supporting jack pistons, apparatus suited to substantially any conditions may be provided. It will be appreciated that the location of the accumulators within the jacks is not essential, and that greater accumulator volumes can be employed if the accumulators are mounted outside, thus providing possibilities of meeting substantially any conditions likely to be encountered.

It will also be appreciated that the preload pressure of the accumulators may be made greater than the normal hydraulic pressure required for roof support, in which event the accumulators would act essentially as safety valves which prevent loss of hydraulic uid. It may be noted that pressure gauges may be applied on various lines to insure correct pressures.

It may be noted, referring to Fig. 10, that the lower frame structures 31 have forwardly extending brackets to which there are suitably secured transversely extending bumper devices which are adapted to engage the conveyor 9 and effect movement of each inclined section of the latter into parallelism with the face, and thus swing an adjacent section about a pivot closely adjacent to the receding end of the coal mining apparatus 2. lf it be desired to apply the conveyor shifting forces at a point midway between the sides of a jack mechanism, a bumper may be supported, by means of pivots 196 providing play for both horizontal and vertical changes in angle of the bumper, upon the forward, lower frame sections 111. The curved forward side 198 of the bumper 195 will provide a very desirable cooperation with the conveyor 9.

An extended discussion of the mode of operation of the jack mechanisms is unnecessary in view of the detailed description. It will be evident that they will be arranged generally perpendicular to the face, and so closely together that extreme loadings of the areas of contact with the roof will be avoided. Instead of the arrangement or spacing shown in Fig. l the jack units may be located with the distances between adjacent wheels on side-by-side jack units the same as the distances between wheels on the individual units. It seems unnecessary to call attention again to the fact that each complete jack unit will have its roof-supporting sections advanced relative to the abutment jack and concurrently push forward a portion of the conveyor line, and then have its abutment jack relieved of pressure and advanced relative to the roof-supporting sections. The roof-supporting jacks will be subjected to hydraulic pressure from the pump 93 in such ak manner that they will provide the desired roof support, and. the forces will be applied to the' roof through the relatively yielding solid rubber tires 116, the

yielding of these tires, as shown in several of the iigures, resulting in substantial areas of contact between the tires and the roof and a diminution f the maximum pressures imposed on the roof at any given point. It will be unnecessary to relieve the pressure in the roof-supporting jacks in order that advance of these jacks may be possible. If the roof pressure suddenly increases, a portion of the fluid below the pistons in the jack devices 33, 33', or whichever one of them may underlie the roof area where the pressure is increased, will be forced into the accumulator, increasing the pressure of the confined nitrogen or other gaseous iluid in the accumulator bag and thereby in many cases enabling continued non-rigid withstanding of the increased roof pressure. When the roof jack underlying the area of increased pressure is advanced from beneath that area the gaseous Huid under increased pressure in the accumulator bag will displace liquid from the accumulator and cause the return of the roof-engaging portions of the jack device to its previous level. Of course, as has been previously explained, before a pressure could be built up in the accumulator sufficient to rupture the bag therein, the relief valve means heretofore described in the connections 109 and/ or 109' would allow the escape of iluid and the substitution of a solid for a yielding support for the roof pressure.

The provision of the yielding support of course facilitates the advance of the jacks over uneven bottom or beneath uneven roof. A feature of the use of turnbuckles 120 lies in the possibility of placing the longitudinal axis of the unit 21 out of line with the longitudinal axis of the unit 22, thereby making possible a change in direction under the action of the feeding cylinder and piston mechanism when this is necessary. The provision of the support elements 174 results in better protection for the area overlying the conveyor and the angle of this supplemental support can be altered readily at any time that the support might, for example, tend to interefere with forward feed. The provision of this kind of protection for the space above the conveyor permits having the areas of roof engagement of the upper wheels directly above the licor-engaging areas of the lower wheels. Further explanation of the mode of operation and advantages of the invention, so far as the embodiment thereof heretofore described in detail, is clearly unnecessary, since the manner of extending the jack devices of the roofsupporting jack mechanisms, the manner of extending and collapsing the abutment jack 23, and the manner of supplying uid to the opposite ends of the cylinder and piston mechanism 24 will be clearly apparent from the description already given.

In Figs. 7 and 8 another arrangement of walking roofsupporting jacks is shown. In this arrangement, instead of having the front and rear roof support jack devices control oor and roof-engaging carriages individual to them, there are but two upper and two lower frames having roof and oor engaging devices on them, one long upper frame at each side, and one long lower frame at each side; and each of the jack devices 201, 202, which correspond respectively to the jackl devices 33 and 33', has its upper and lower transversely extending frames 203 rigidly connected at their opposite ends with elongated guide frames 205. There are thus two upper guide frames and two lower guide framesthe frames of each pair being spaced by the width of the cross frames 203 from each other. The guide frames 205 may be of any suitable construction, for example, of rail or generally I-beam construction, being herein shown as formed by rail sections with semi-circular guide elements 206 at `their opposite ends, the guide elements 206 at one end of each guide frame being relatively adjustable to insure suitable tension for the roller connecting elements shortly to be described. The lower frames 205 have shallow channel sections 207 suitably secured, as by welding or otherwise, to their heads and have their base iianges provided with side ledges `208 to provide-for-the lateral guiding of a series of rollers 211 which are adapted to provide a rolling support for the lower frames 205 as the jack mechanism is advanced. The inverted upper rail elements of the upper frames 205 have side ledges 209 at their tops to guide the associated rollers 211, and to support the lower run of rollers associated with the upper guide frames 205, there is disposed beneath them and spaced beneath the bottom of each upper guide frame 205, an elongated guide strip or channel bar 220 which is held in the desired spaced relation to the frame 205 which is above it, by spacing plates 221 secured to the guide bars and to the sides of the frames 205. The rollers 211 are provided with through pins 212 and between these pins and the rollers there are mounted suitable bearings, not shown. The opposite ends of the pins are bored as shown in Fig. 7 at 213 to permit a cable 215 to extend through the various openings and provide a connection between the rollers, and in order that the rollers may not contact with each other, these pins maybe xed to the cable loop as by axial clamping screws 216.

The devices for expanding the jack elements, the devices for feeding them, etc., maybe the same as in the first described embodiment of the invention. It may be noted .that the abutment jack 23 may be repositioned laterally, as indicated in dotted lines in Fig. 7, as is also true in the case of the abutment jack 23, of the rst embodiment, so as to cause the jack devices to change their direction of travel, that is, to be moved slightly laterally in one direction or the other as they advance toward the face. It will be understood that the mountings of the upper frames 203 on the jack devices 201, 202 permits lateral and longitudinal tilting of the solid upper frame structure including two frames '203 and two framesV 205.

This specification need not he extended by further exposition of the structure or the advantages of the invention as this would result mainly in repetition, though in diiferent forms, and it will suffice to call attention to the fact that Fig. 9 shows the first embodiment described, in use, illustrates the jack shown as ready to move up and advance a section of the conveyor when the machine 2 is out of the way, shows the protection of the space above the conveyor, shows the caved roof acting on the rails 171, and the roof between the caved section and the face supported by the walking jack. Of course there are other jacks, not sho-wn, at either side of the one illustrated.

While there are in this application specifically described two forms which the invention may assume in practice, it will be understood that these are disclosed for purposes of illustration and that the invention may be modiied and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

l. In a walking jack mechanism, a pair of mutually longitudinally spaced elongated frames each having at points widely spaced longitudinally thereof devices for engaging a mine floor with rolling contact, a second pair of mutually longitudinally spaced elongated frames each having at points widely spaced longitudinally thereof devices for engaging a mine roof with rolling contact, the frames of said second pair overlying the frames of said first pair, hydraulic jack devices one supported on each of said rst pair of frames and `supporting the one of said second pair of frames which overlies the frame on which such jack device is supported, an abutment jack disposed between said other jacks and including mine door and mine roof engaging elements and means for forcing them apart to fix said abutment jack tightly between mine floor and roof, an extensible device between one of said first mentioned jack devices and said abutment jack for advancing them in succession, and connections Toetween the mutually adjacent ends of the individual frames of each pair of frames providing for relative angular movement between the connected `frames while precluding their separation beyond a predetermined distance. v

l2. -In a VVwalking jack mechanism, a 'pairof 'mutually longitudinally spaced elongated iframes each having l'at each side thereof at points widely spaced longitudinally thereof devices for engaging a mine iloor with rolling contact, a `second pair of mutually longitudinally spaced elongated frames each having at each side thereof at points widely spaced longitudinally `thereof devices for engaging a mine roof with rolling contact, ythe ramesof said second pair overlying the frames-of said `first pair, hydraulic jack devices one supported -on each of said first pair or" frames and supporting the one of said second pair of frames which overlies the frame onwhich 'such jack device is supported, -an abutment jack disposed between said other jacks and including mine `floor and mine roof engaging elements and means for forcing them apart to fix said abutment jack tightly between mine floor and roof, a device between one of Said iirst mentioned jack devices and said abutment jack for advancing them-in succession, and connections between 'the longitudinally spaced individual frames of each 'pair for limiting their separation and securing them together for concurrent movement, said connections being spaced apart laterally and individually adjustable in length.

3. In a walking jack mechanism, a pair of longitudinally spaced frames each having thereon a device for engaging a mine roof with rolling contact, a pair of longitudinally spaced frames underlying said first pair of frames and each having a device 'engaging a mine floor with rolling contact arranged to support it forV movement over a mine floor, hydraulic jack devices' supported one on each of said last recited frames' and supporting the overlying one of said iirst mentioned frames', an abutment jack disposed between said other jacks and engageable with the mine floor and roof and extensible to eiect its anchoring firmly between the same, an expansible and contractible device between one of saidiirst mentionedjacks and said abutment jack for advancing them in succession, and connections for causing the framesof each pair to move together, each of said hydraulic jack deviceshaving an accumulator enclosed within it and subjectedly spaced frames underlying said first pair of framesand' each having a device engaging a mine door with rolling contact arranged to support it for movement over a mine oor, the oor engaging devices substantially directly underlying the roof engaging devices, hydraulic jack devices supported one on each of said last recited frames and supporting the overlying one of said rst' mentioned frames, an abutment jack disposed between said hydraulic jack devices and engageable with the mine oor and roof to anchor it in position, a device betweenv one of said first mentioned jacks and said abutment jack for advancing them in succession, connectionsfor causing-theframes of each pair to move together, one ahead of the other, and means adjustably mounted on and projecting forwardly from the forward upper frame to overlie a space ahead of the forward lower frame.

5. ln a walking jack mechanism, a pair of mutually longitudinally spaced frames each having at least adjacenty its opposite ends devices for engaging a mine oor with rolling contact, a second pair of mutually longitudinally spaced frames each having at least adjacent its opposite ends devices for engaging a mine roof with rolling contact, l

the` frames of said second pair overlying the frames of said tirstv pair, hydraulic jack devices supported on each of said first pair of frames and supporting the one of said second pair of frames which overlies the frame on which it is itself supported, an extensible abutment jack disposed' between said other jacks and engageable with the mine ilocr and roof to hold it rigidly in positiong-a device between one'of said lirst mentioned' jack devices `and-'said abutment jack for: advancing-@themf-in turn; and, connec- 12 tions `'between the vframes of e'ach pair forcasin'g'them to move -together, each of said hydraulic jack devices having within the same-chamber-forming.means confining a body of entrapped Sgas and having 'a-movable wall subjected on opposite-sides to thepres'sure of 'the entrapped fluid and to the saine pressures that prevail in said jack.

6; In a walking jack mechanism, a plurality of longitudinally spaced'roof 4supporting jacks and an intermediate abutment jack, said several jacks arranged in a rov'v extending in their intended direction of advance and each of said roof supporting jacks having associated with it longitudinally extending frames respectively equipped with devices for rolling contact with mine tloor'and mine roof, a cylinder and piston mechanism having a cylinder connected to one ofsaid roof supporting jacks and a piston rod rigidly connected to said abutment jack, and means' operatively connecting the second of said roof supporting'jacks for movement with the iirs't including connections between the mutually adjacent ends of the frames equipped with devices for rolling contact with the mine door and other connections between vthe mutually adiacent ends of the frames equipped with devices for rolling contact with the mine roof.

7; In a walking jack mechanism', a plurality of spaced, forwardly and rearwardly disposed roof supporting jacks and an intermediate abutment jack, a cylinder and piston mechanism having a cylinder connected to one of said roof supporting jacks and a piston rod connected to said labutment jack, and means for operatively connecting the` second of said roof supporting jacks for movement with' the'rst and for limiting the minirnurndistance apart- 'of said forwardly and rearwardly spaced roof supporting jacks including turnbuckles `pivotally yconnected to said forwardly andi rearwardly spaced roof supporting jacks onparallel axes;

8; In a Walking-jack mechanism, a-plurality of spaced, forwardly and rearwardly 4disposed roof supporting' jacks and an intermediate abutment jack,said several jacks disposed in a row extending in' the direction of their intended advance, a cylinder and piston mechanism -ha'vinga cylinder having-a' head support connected at a iiXed height to one of said roof supporting jacks and a piston rod rigidly connected to said abutment ljack, and common means' for connecting 'thesecnd of saidv roof supporting jacks for bodily' advancing movement' with the iirst and for limiting theY minimum distance apart of `said roofsupporting jacks.

9. In a mine roof supporting jack mechanism, an upper roof-engaging device, a'lower'- floor engagingdevic'e, each of said devices including a frame carrying roller means, saidroller means having 'rolling contact withV thetloor and roof, an extensible jackmechanism arrangedibet'ween said frames-for" elevating'saidro'of engaging'device into roof supportingposition, said extensible jack` 1r1ccha'nisn`1v including a hydraulically controlled cylinder and piston mechanism and having in' communication with the in-` teiior'thercof chamber-forming means confining a body of` entrapped gaseous iluid and subjected to the hydraulic pressure within said jack and ofgsmaller cross sectional area than the workingv cross sectional arca'of said cylin-v der and piston mechanism and power operated Vmeans associated with said jackmechanism yfor'moving said devices horizontally in unison while they are maintained infsuppor'tin'g relation-,with the roof and'tloor, and said roller-means rolling-along the'roof andl door during'such horizontal movement. K V

l0. In' a1 minej roof supportingjack'niechanism, an upper roof engaging device, -ailowerloor engaging device, each -ofsaid devices including afraruev carrying roller means', said roller means having'rolling contact with `the door androof, an extensible jack mechanism arranged between said? frames for elevating said *roof engaging'device' into-'roof `supporting position, :said extensible' jack mechanism including-a hydraulically-controlled `cylinder s and piston-mechanism fand-h'avingf-incommunication with' the interior thereof chamber-forming means conning a body of entrapped gaseous uid and subjected to the hydraulic pressure within said jack and of smaller volumetric capacity than the volumetric capacity of said cylinder and piston mechanism, and power operated means associated with said jack mechanism for moving said devices horizontally in unison while they are maintained in supporting relation with the roof and door, and said roller means rolling along the roof and floor during such horizontal movement.

l1. In a mine rool` supporting jack mechanism, an upper roof engaging device, a lower oor engaging device, each of said devices including frames arranged in parallel vertical planes and carrying roller means, said roller means having rolling contact with the door and roof, an extensible jack mechanism arranged between said devices for elevating said roof-engaging device into roof supporting position, said roof-engaging device including a transverse frame between its roller means carrying frames, means for supporting said transverse frame on said extensible jack mechanism for rocking on a longitudinal axis and means for connecting said tirst mentioned frames to said transverse frame to rock on a transverse axis, and power operated means associated with said jack mechanism for moving said devices horizontally in unison while they are maintained in supporting relation with the roof and oor, and said roller means rolling along the roof and floor during such horizontal movement.

12. In a mine roof supporting jack mechanism, a front roof jack device, a rear roof jack device, each of said devices including upper and lower frames carrying roller means having rolling contact with the roof and door, an extensible jack mechanism for elevating said upper frame to bring said upper roller means into supporting relation with the roof, adjustable connections between the sides of the frames of said jack devices and variable in length for varying the laterial angular relation of said devices, and power operated means associated with said front jack device for moving said jack devices horizontally in unison while the same are maintained in supporting relation with the roof and oor, and said roller means rolling along the roof and floor during such horizontal move- 14 ment, and said adjustable connections being adjustable to vary the angular relation of said jack devices to facilitate steering as they are moved horizontally as aforesaid.

13. In a mine roof supporting jack mechanism, a front roof jack device, a rear roof jack device, each of said device including upper and lower frames for respectively traversing the roof and floor, an extensible jack mechanism for elevating said upper frame into supporting relation with the roof, adjustable connections between the upper trames and between the lower frames of said jack devices respectively, variable in length for varying the spacing of said devices, and power operated means associated with one of said jack devices for moving said jack devices horizontally in unison while the same are maintained in supporting relation with the roof and floor.

References Cited in the le of this patent UNITED STATES PATENTS 76,419 Donisthorne Apr. 7, 1868 81,759 Donisthorne Sept. 1, 1868 881,609 Nellen et al Mar. 10, 1908 942,170 Dunlap Dec. 7, 1909 1,480,733 Morgan Ian. 15, 1924 1,486,293 Morgan Mar. 11, 1924 1,588,987 OToole June 15, 1926 1,704,866 Morgan Mar. 12, 1929 1,736,853 Fisher NOV. 26, 1929 1,765,200 Bullough June 17, 1930 1,998,294 Thomas et al Apr. 16, 1935 2,256,835 Mercier Sept. 23, 1941 2,313,242 Johnson Mar. 9, 1943 2,352,390 Kirkland June 27, 1944 2,420,666 Joy et al. May 20, 1947 2,420,755 Mavor May 20, 1947 FOREIGN PATENTS 512,214 Germany Nov. 10, 1930 543,896 Germany Feb. 11, 1932 511,557 Great Britain Aug. 21, 1939 

